1. Field of the Invention
The present invention pertains to a device for damping vibrations. The invention more particularly concerns the reduction or elimination of vibrations of a hub contained within an automotive clockspring.
2. Discussion of the Background
Devices are well known in the art for damping the sound emanating from automobile clocksprings due to the vibration of the hub or rotor contained within the clockspring housing. An automotive clockspring is an electrical connector or rotary transducer which electrically connects a rotatable airbag assembly mounted on the steering column to stationary crash sensors located elsewhere on the vehicle. An automotive clockspring typically includes a housing and a cover mounted to the housing so as to from a cavity therebetween. Rotatably mounted within the cavity is a hub. The clockspring housing is non-rotatably mounted to the steering column, while the hub is attached to the rotatable airbag assembly. Electrical cable is typically wound around the hub. One end of the electrical cable terminates at the stationary housing or cover and the other end terminates at the hub. The end of the electrical cable terminated at the hub is then connected to an electrical cable which connects to the airbag assembly. During use, the electrical cable is either spooled or un-spooled around the hub when the steering wheel is turned in one direction or the other direction.
It is desirable to have a clockspring which requires very little torque to rotate the hub relative to the stationary housing and cover. Any increase in torque is felt by the driver of the vehicle as rotational resistance of the steering wheel when the steering wheel is rotated. One way of reducing the torque is to provide a clearance fit between the hub and both the housing and the cover within the cavity. Such a clearance fit allows the hub to freely rotate, with little applied torque, within the cavity of the clockspring. A drawback of such a solution is that the hub vibrates and moves around, translationally, within the provided clearance and contacts the housing and cover. The resulting contact is perceived as undesirable audible noise within the passenger compartment of the vehicle. The source of the vibratory energy that causes the hub to vibrate can be from the rotation of the steering wheel or it can be from vibrational energy passing through the steering column from the engine, chassis or wheels.
One solution to reduce the noise, while maintaining the clearance between the hub and the housing, is to place a lubricant within the clearance of the clockspring. Typically the lubricant is a liquid, a solid carried by a solvent, or a solid material which is either malleable or is in many small pieces (i.e., for example, graphite particles). The lubricant dampens the motion of the hub through the clearance, since the hub must physically displace the lubricant before the hub contacts the housing or cover. Disadvantages of this solution are that the viscosity of lubricants generally greatly increases as the temperature decreases, thus greatly increasing the torque required to rotate the hub; and with time and use lubricants tend to migrate out of the clearance, which results in undesirable vibration of the hub. Furthermore, assembling clocksprings with a lubricant adds to the complexity of the assembly process by handling the lubricant which fouls the workplace, increases the number of parts, and increases the cost of the finished product.
Thus, there is a need for a low cost, reliable, and simple to manufacture clockspring which does not generate audible vibratory sounds.